
where \(\chi =L_{\mathrm {FUV}}/L_{\star }\)  [1]}. For early B stars and late O stars (\(T_{\mathrm {eff}}\simeq 2.5\text{-}4.0\times 10^4\,\mathrm {K}\) ), \(\chi \simeq 0.5\)  [2]}. We estimate the central star's luminosity assuming it is re-radiated in dust continuum emission. In M42, we have \(L_{\mathrm {FIR}}\simeq 1.5\times 10^5\,L_{}\) , hence theory predicts \(G_0\simeq 1.5\times 10^3(1\,\mathrm {pc}/d)^2\) . From the data associated with OMC4, we estimate \(G_0\simeq 500(1\,\mathrm {pc}/d)^2\)  (Fig. REF  and Table REF ). As we have shown in Paper I, from the data for the edge-on PDR in the Eastern Rim we also estimate \(G_0\simeq 500(1\,\mathrm {pc}/d)^2\) . This discrepancy between the theoretical and observed relations is likely caused by the geometry of the Orion Nebula. The close adherence to a \(d^{-2}\)  law illustrates that the continuum emission is due to dust predominately heated by the central massive stars.
